.\"	$OpenBSD: mem.4,v 1.3 2007/05/31 19:19:53 jmc Exp $
.\"
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.\"	from: @(#)mem.4	5.3 (Berkeley) 5/2/91
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt MEM 4 amd64
.Os
.Sh NAME
.Nm mem ,
.Nm kmem
.Nd memory files
.Sh DESCRIPTION
The special file
.Pa /dev/mem
is an interface to the physical memory of the computer.
Byte offsets in this file are interpreted as physical memory addresses.
Reading and writing this file is equivalent to reading and writing
memory itself.
Only offsets within the bounds of
.Pa /dev/mem
are allowed.
.Pp
Kernel virtual memory is accessed through the interface
.Pa /dev/kmem
in the same manner as
.Pa /dev/mem .
Only kernel virtual addresses that are currently mapped to memory are allowed.
.Pp
On amd64, physical memory is discontiguous; especially,
the ISA I/O memory space covers the physical address range from
.Li 0x000a0000
to
.Li 0x00100000 .
.Pp
The kernel virtual memory begins at address
.Li 0xffffffff80000000 .
.Pp
Writeability of these devices is controlled by the system
.Xr securelevel 7 .
.Sh FILES
.Bl -tag -width Pa -compact
.It Pa /dev/mem
.It Pa /dev/kmem
.El
.Sh SEE ALSO
.Xr securelevel 7
.Sh HISTORY
The
.Pa /dev/mem
and
.Pa /dev/kmem
files appeared in
.At v6 .
